Google just released a set of Android Auto developer documents to developer.android.com, detailing more of Google's in-car platform and giving developers a better sense of the system's capabilities.

Android Auto "apps" aren't really apps; they're additional Android Auto-specific content that developers add to their existing Android apps. This is exactly the way Android Wear works. Developers don't have separate phone, watch, and car apps; they just include additional interface attributes in their regular apps for display on the other form factors.

Further Reading

Developers don't get to design interfaces in Android Auto, it's more of a "fill-in-the-blanks" style of development. Google makes the interface layout, and developers get to change the colors, button actions, and text of that interface. Apps also provide a content stream for playback, but that's pretty much it.

Developers can't touch the layout of an app. They can't move buttons around, add additional buttons, change the size of things, or add additional screens. If you want to build something Google's hasn't considered—like say, a speedometer app—it appears impossible for now. The above gallery has a few examples of Google's generic design followed by a customized version.

Since developers are limited to coloring within Google's lines, it's important to look at what interfaces Google has made available to plug into. Android Auto has "media app" interface—basically a music player—which developers can use for "music, podcast, live radio, and audio news apps." Like Android Wear, Auto will plug into the Notification APIs and automatically pick up notifications and display them in a "car appropriate" manner on the vehicle screen. There will be a set of voice actions that apps can register for, and there's also an app list.

Apps have a "night mode" which will switch over to a darker color palette so drivers aren't blinded at night. Additionally, there will be some kind of content library UI, which wasn't pictured.

Further Reading

Presumably, the lack of developer control over apps and app design boils down to one important feature: safety. Google has enlisted the help of the National Highway Traffic Safety Administration to design Android Auto so it's not distracting. While you always hope drivers pay more attention to the road than the car computer, a frustrating piece of custom UI could potentially cause an accident. As such, Google says it's aiming for a simple, glanceable UI, and it recommends developers pare down their app features to keep everything "safe and drive-appropriate."

Google says the standardized UI is to placate the various regulatory bodies around the world. "Android Auto provides you with a standard UI designed to minimize driver distraction," the company explains. "You do not have to test a custom UI for driver distraction, which is a lengthy and expensive process involving multiple legislations across the globe and different standards for each vehicle OEM."

So developers, don't dream too big, because it looks like there isn't much you'll be allowed to do on Android Auto. We'll have more information once we actually get our hands on the SDK, which Google says will be released in "the coming months."

Ron Amadeo
Ron is the Reviews Editor at Ars Technica, where he specializes in Android OS and Google products. He is always on the hunt for a new gadget and loves to rip things apart to see how they work. Emailron@arstechnica.com//Twitter@RonAmadeo